1. Field of the Invention
This invention relates generally to vehicular seat belt retracting mechanisms, and more specifically, to an apparatus for selectively eliminating the retractive tension of the belt upon the wearer.
2. Prior Art
The last decade has seen the universal provision in almost all passenger vehicles of safety belt mechanisms to restrain the passengers safely within the vehicle during emergency conditions, such as collisions or sudden stops.
Typically, these belt systems are provided with a flexible safety belt which extends across the lap and chest of the wearer and interconnects with the frame of the vehicle, usually with a quick-disconnect buckle, to restrain the passenger in a "buckled-up" position, i.e., seated comfortably in a vehicle seat and reclining against a backrest.
Usually, the belts are retained on a spool rotatably-attached to the frame of the vehicle and continuously biased in a belt-retractive direction by means of a coil spring, such that, when the belt is unbuckled, the belt withdraws to a fully-retracted position and out of the way of the passenger. Additionally, it may be provided that the extensive end of the belt be attached to, for example, the door of the automobile, such that the step of opening the door extends the belt out of the way of the passenger for entry into the vehicle, and the step of closing the door permits the belt to retract to its retentive position about the wearer.
Typically, the retractor mechanism is provided with a means for sensing accelerations of the vehicle and/or accelerations in the belt of a level occuring during emergency conditions and for locking the spool against further extensive movement, thereby preventing further extensive movement of the belt and restraining the passenger during the occurrence of the emergency.
Devices for relieving retractive tension in vehicle safety belt mechanisms are known in the art.
U.S. Pat. No. 3,834,646 to Heath describes a retractor mechanism that includes a vehicle sensitive inertial lock-up and an automatic tension-relieving mechanism. The mechanism utilizes a pawl that rides on the edge of a pair of cam disks rotated by a retractor spool and arranged such that the pawl will fall into engagement with the spool ratchet surface upon a sequence of belt extension, retraction, and a subsequent predetermined extension. This sequence of belt manipulation automatically initiates the tension-relieving mode and automatically resumes the tension mode upon subsequent extension.
U.S. Pat. No. 4,200,311 to Fisher teaches another form of automatic tension-relieving mechanism that includes a memory by utilizing a pawl engagable with a disk attached to the retractor spool and having multiple groove tracks. Upon substantial extensive movement of the spool, followed by retraction, a pawl is engaged in a multiple track engagement, whereby subsequent extension will cause the pawl to engage and be retained by multiple ratchet teeth corresponding with desirable amounts of belt slack and preventing subsequent retraction of the belt beyond the point of engagement. The tracks are spiral grooved but allow a moderate amount of belt extension without the pawl becoming disengaged from the groove, such that upon retraction, the pawl will retrace its outwardly-spiraling path and will become re-engaged with the ratchet teeth and with substantially the same amount of slack, thus having memory.
U.S. Pat. No. 4,293,107 to Ziv discloses a retractor spool having one of a pair of mutually engaging ratchet disks fixedly mounted thereto, the second being carried by an extended length portion of the spool shaft such that it is laterally slidable along the shaft into and out of engagement with the first disk. An orienting spring biases the second disk to engagement with the first disk and rotationally re-orients the second disk into a pre-determined initial condition upon disengagement from the first disk. Disengagement is accomplished by a lifting plate that interconnects with the collar and sleeve portion of the second ratchet disk to lift it out of engagement. Integral with the second ratchet disk is a memory disk having an open outwardly-spiraling groove that interacts with a tension-relieving pawl and an orienting pawl. The tension-relieving pawl is biased to track the radially inward wall of the groove and is engageable with multiple tension-relieving teeth carried by the inward wall of the groove to prevent retractive rotation of the spool. The tension relieving pawl is also lifted by a lifting plate such that the pawl springs radially inward against an orienting stop so that the pawl will reengage the disk groove in a predetermined orientation. A lever communicates with the lifting plate to cause the mechanism to be engaged or disengaged from the retractor spool. A latch is provided to retain the actuator lever in the engaged position until either manual override or extension of the belt beyond the predetermined maximum amount causes the tension relieving pawl to cause an extended length disengaging arm of the latch to unlatch the actuator lever.
One of the problems encountered with the prior art tension-relieving mechanisms is that of the increased number of frictional surfaces associated with the mechanisms, which result in an increased drag on the spool in the retractive direction, and hence, larger retractor springs and forces, as well as an increased complexity and cost related to control over the finish on the fricitional surfaces, the degree of lubrication required, and wear.
Another problem with the prior art mechanisms is that they provide only a limited amount of "freedom" in movement of the wearer beyond the "slack" position before unlocking the reel to a retractive movement below the memory position. Typically, this occurs after only one or two revolutions of the spool at most, which translates into only a few millimeters of freedom of movement to the wearer through which the mechanism can "remember" the slack position.
It would be desirable, therefore, to provide a tension-relieving apparatus for a safety belt retractor mechanism which is also relatively frictionless, which is relatively inexpensive and simple to fabricate and assemble, yet which is reliable in operation, and which permits a greater amount of extensive movement of the belt above the slack position before unclocking the apparatus from the tensionless mode.